Asda
Not quite right I'm afraid. The scheme is protected through the protection to the Trust Deed afforded by the Transport Act and that protection applies to all members whenever they joined so they can't reduce the benefits of anybody who is already a member.
The Trust of Promise stops them forcing anybody out of the scheme. That only applies to those who were in the scheme in July 2001. The continuation of the Trust of Promise must be a condition if NATS is sold in the normal way so that protection would continue if NATS is sold but, very importantly, the Trust of Promise does not apply if NATS goes bust. Currently post PPP members have some rights to continuation in the scheme afforded by TUPE and other legislation which protects your terms and conditions but not as much as pre PPP members. If NATS goes bust we all have the same legal protection. The Memorandum of Understanding will probably give post PPP members a bit more protection than they currently have but as nobody has actually seen this proposed document we can't know for sure.